1. Field of the Invention
The present invention relates to a liquid-jet head which ejects jets of liquid, a manufacturing method thereof and a liquid-jet apparatus. More particularly, the present invention relates to an ink-set recording head which ejects ink droplets by displacement of piezoelectric elements formed on surfaces of vibration plates partially constituting pressure generating chambers communicating with nozzle orifices ejecting ink droplets, to a manufacturing method thereof and to an ink-jet recording apparatus.
2. Description of the Related Art
In an ink-jet recording head, in which pressure generating chambers that communicate with nozzle orifices ejecting ink droplets are partially constituted of vibration plates, these vibration plates are deformed by piezoelectric elements to pressurize ink in the pressure generating chambers, and the ink droplets are ejected from the nozzle orifices, two types of recording heads are put into practical use. One is a recording head using piezoelectric actuators of a longitudinal vibration mode, which expand and contract in an axis direction of the piezoelectric elements, and the other is a recording head using piezoelectric actuators of a flexural vibration mode.
In the former one, a volume of each pressure generating chamber can be changed by abutting an end surface of the piezoelectric element against the vibration plate, and manufacturing of a head suitable to high density printing is enabled. On the contrary, there is required a difficult process of cutting and dividing the piezoelectric element in a comb tooth shape in accordance with an array pitch of the nozzle orifices and work of positioning and fixing the cut and divided piezoelectric elements to the pressure generating chambers. Thus, there is a problem of a complex manufacturing process.
On the other hand, as the latter ink-jet recording head, in Japanese Patent Laid-Open No. Hei 5 (1993)-42674, proposed is one, in which a vibration plate is laminated on a passage-forming substrate with pressure generating chambers provided thereon by adhesion or diffused junction and piezoelectric elements are adhered onto this vibration plate with an adhesive agent applied therebetween.
The adhesion of the piezoelectric elements and the vibration plate with the adhesive agent applied therebetween leads to a problem that, because of insufficient interfacial bonding between the piezoelectric elements and the adhesive agent, the piezoelectric elements are likely to be peeled off from the vibration plate by repetitive deformation of the piezoelectric elements. In order to solve the above problem, in Japanese Patent Laid-Open No. Hei 5 (1993)-42674, a constitution is disclosed as a conventional example, in which, in order to make the peeling off of the piezoelectric elements from the vibration plate unlikely to occur, an amount of the adhesive agent used for the adhesion of the piezoelectric elements and the vibration plate is enlarged and the adhesive agent is largely raised on a side of the piezoelectric element.
In Japanese Patent Laid-Open No. Hei 5 (1993)-42674, with the conventional constitution in which the adhesive agent is largely raised on the side of the piezoelectric element, there is a problem as below. Specifically, use of an insulating adhesive agent deteriorates conductivity, thus causing a need to increase a voltage applied to the piezoelectric element and inhibiting durability of the piezoelectric element, and use of a conductive adhesive agent is unsuitable for adhesion of the piezoelectric element because of its weak adhesion strength. In order to solve the above problem, a thin film of a coupling agent is formed on a vibration plate and the piezoelectric element is adhered to the vibration plate by injecting the insulating adhesive agent into a gap between the coupling agent and the piezoelectric element or therearound.
Moreover, in Japanese Patent Laid-Open No. Hei 9 (1997)-234864, there is proposed an ink-set recording head, in which piezoelectric elements are adhered onto a vibration plate with an adhesive agent interposed therebetween.
In this gazette, disclosed is a constitution, in which a reinforcement plate made of a metal plate with high rigidity is joined or adhered onto a passage-forming substrate, in which pressure generating chambers are formed, and a piezoelectric element is adhered onto this reinforcement plate with an adhesive agent interposed therebetween so that one of the electrodes of the piezoelectric element (a lower electrode) is electrically conducted to the reinforcement plate. In the disclosed invention, in order that the piezoelectric element is joined in such a way that one of the electrodes thereof directly contacts the reinforcement plate, the piezoelectric element and the reinforcement plate are adhered to each other by providing an adhesive agent in a square portion defined by a boundary between a side face of the piezoelectric element and the reinforcement plate.
Furthermore, in Japanese Patent Laid-Open No. Hei 6 (1994)-106724, there is proposed a constitution, in which a piezoelectric element is adhered onto a vibration plate with an adhesive agent interposed therebetween.
In this gazette, disclosed is a constitution, in which a vibration plate is joined onto a passage-forming substrate with an epoxy adhesive interposed therebetween, a piezoelectric element is joined onto this vibration plate with an epoxy adhesive interposed therebetween and a FPC is joined onto the piezoelectric element with a conductive adhesive agent interposed therebetween. When the conductive adhesive agent used in joining the piezoelectric element and the FPC protrudes over a side face of the piezoelectric element, both electrodes of the piezoelectric element are short-circuited. So as not to allow the short-circuiting to occur, the epoxy adhesive, which is used for the adhesion of the passage-forming substrate and the vibration plate and the adhesion of the vibration plate and the piezoelectric element, is made to protrude over the side faces of the piezoelectric element and the vibration plate to cover the both thereof with its surface tension.
There is a method in which the piezoelectric elements are fabricated and installed on the vibration plate by a relatively simple process of adhering a green sheet as a piezoelectric material while making a shape of the green sheet fit to that of the pressure generating chambers, and sintering the green sheet. However, with the constitution of adhering the piezoelectric elements on the vibration plate, a certain area of the vibration plate is required due to use of the flexural vibration, thus there is a problem that a high density array of the piezoelectric elements is difficult.
Meanwhile, in order to solve such a disadvantage of the latter recording head, as described in Japanese Patent Laid-Open No. Hei 5 (1993)-286131, a recording head is proposed, in which an even piezoelectric material layer is formed over the entire surface of a vibration plate by a deposition technology, the piezoelectric material layer is cut and divided into a shape corresponding to that of pressure generating chambers by a lithography method, and piezoelectric elements are formed so as to be independent of each pressure generating chamber.
The recording head described above has the following advantage. The work of adhering the piezoelectric elements to the vibration plate is eliminated, and the piezoelectric elements can be fabricated and installed by the lithography method, which is a precise and simple method. In addition, a thickness of each piezoelectric element can be thinned to enable a high-speed drive.
Moreover, in general, a sealing plate which has a piezoelectric element holding portion and seals the piezoelectric element is joined onto the piezoelectric element-facing surface of a passage-forming substrate on which pressure generating chambers are formed. By hermetically sealing this piezoelectric element holding portion with inert-gas and the like, damage to the piezoelectric elements attributable to an external environment is prevented.
However, in a miniaturized and high-density ink-jet recording head, since a wide head area cannot be secured, there is a problem as below. Specifically, a sealing hole which is for filling and hermetically sealing the piezoelectric element holding portion with inert-gas and the like, and through which the piezoelectric element holding portion provided on the sealing plate communicates with the outside becomes small, and thus it is difficult to completely hermetically seal the piezoelectric element holding portion.
Moreover, in the high-density ink-jet recording head, in order to thin the thickness of the piezoelectric element, a gap between the upper and lower electrodes is narrowed. Thus, there is a problem that a surface discharge occurs in a portion of an end surface of the piezoelectric element where the electrodes are exposed, and so a withstand voltage of the piezoelectric element is lowered.
Furthermore, in order to dispose piezoelectric elements and nozzle orifices in high density, there is a constitution in which a vibration plate is formed on a passage-forming substrate not by use of an adhesive agent but by deposition, thus obtaining a thin film. However, there is a problem that, in a square portion defined by a boundary between a side face of the piezoelectric element and the vibration plate, a crack is likely to occur in the vibration plate, ink in the pressure generating chambers flows towards the piezoelectric element via the crack and thus the piezoelectric element is damaged.
Note that, needless to say, such problems as described above similarly exist not only in the ink-jet recording head ejecting ink but also in another liquid-jet head ejecting a liquid other than ink.